Experiment shows bacteria can live under intense pressure, life might thrive under extreme conditions

Updated:
Thursday, February 21, 2002 12:00 AM EST

WASHINGTON (AP) _ Common bacteria survived under almost a quarter-million pounds of pressure in an experiment that suggests microbes may live in extreme environments on Earth and in the solar system where life was thought impossible, researchers say.

In a study appearing Friday in the journal Science, scientists at the Carnegie Institution report that when they squeezed bacteria between the jaws of a diamond anvil at up to 17,000 times normal atmospheric pressure, some of the microbes were able to live and consume their chemical diet.

It was the first scientific demonstration that common bacteria could adapt to such pressures and survive, said Anurag Sharma, the first author of the study.

``Since these microbes could adapt to such extreme pressures, this suggests that when we look for life in places beyond the Earth, we have to look beneath the surfaces,'' said Sharma. ``The habitable zone is now expanded.''

Dr. Kenneth Nealson, a geobiologist at the University of Southern California and a researcher at NASA's Center for Life Detection at the Jet Propulsion Laboratory, said the implications of Sharma's research ``knocked my socks off.''

``When you realize that organisms could function at pressures equivalent to many kilometers beneath the surface of the Earth, it extends the limits of life,'' said Nealson. ``It has very interesting implications for the potential of life for places like Jupiter and other large planets where the gravity is so immense.''

In recent years, researchers have found bizarre Earth organisms, generally called ``extremophiles,'' that thrive in very hostile conditions of extreme heat, dryness, radiation and acidity. Microbes have been found at the bottom of the ocean around volcanic vents, in polar ice and in boiling pools.

The new study adds pressure to the list of extremes where life can persist.

``It extends the limits of life to another zone that we hadn't thought of before,'' said Nealson. ``This really expands where we think life might be able to survive in the universe.''

In the study, Sharma, biologist James Scott and their colleagues used a diamond anvil to test the resilience of two common microbes, E-coli, found in the human gut; and Shewanella oneidensis, ordinary bacteria that live in muck beneath shallow waters of Oneida Lake near Syracuse, N.Y.

The anvil is a device that squeezes two gem-quality diamonds against each other at very high pressures. Sharma said the microbes, mixed with water and a chemical called formate, were placed inside a dimplelike depression between the jaws of the anvil.

As the anvil closed, pressure was applied directly on the mix of microbes and fluid.

When the pressure reached about 174,000 pounds per square inch, the water in the mix turned to a crystal called ice-6.

``We squash the atoms so close together that liquid water turns into a solid at room temperature,'' said Sharma. Ice-6 is much denser than ordinary ice and will remain a solid only under pressure.

Eventually the diamond anvil pressure reached about 249,000 pounds per square inch. The researchers kept it at that pressure for hours before retrieving the specimens.

Sharma said chemical tests showed that about 1 percent of the one million bacteria squeezed in the anvil survived. The tests also showed that the bacteria continued to metabolize the formate, turning some of the chemical into carbon dioxide and hydrogen.

Even though some of the microbes survived, the study suggested they were not happy campers. Sharma said some had deformed into weird shapes. There also was no indication that the bacteria could reproduce at the high pressures.

``They could metabolize at those pressures, but they didn't have the capability to divide as they could at lower pressures,'' said Sharma.

Sharma said the experiment suggests that when NASA searches for life in outer space, the agency should consider sites that might have previously been ignored because they had such high pressures.

He suggested deep waters on the moons of Jupiter or far below the surface of the Martian ice caps as possible areas where life could be sustained.

``Our study has direct implications about the feasibility of life in extreme environments that were previously thought to be inhospitable,'' said Sharma.